In recent years, advances in technology, as well as ever evolving tastes in style, have led to substantial changes in the design of automobiles. One of the changes involves the power usage and complexity of the various electrical systems within automobiles, particularly alternative fuel vehicles, such as hybrid, electric, and fuel cell vehicles.
Many of the electrical components, including the electric motors used in such vehicles, receive electrical power from alternating current (AC) power supplies. However, the power sources (e.g., batteries) used in such applications provide only direct current (DC) power. Thus, devices known as “power inverters” are used to convert the DC power to AC power, which often utilize several of switches, or transistors, operated at various intervals to convert the DC power to AC power.
Often, a capacitor is configured electrically in parallel between a DC energy source and the power inverter in order to reduce voltage ripple. In a standard three-phase inverter, the filter capacitor current is a function of the modulation index and output current. This capacitor, often referred to as the DC link capacitor or bulk capacitor, must have a large enough capacitance and power rating to handle a peak RMS ripple current during operation. Often, the capacitor current limits the ability to shrink the size and cost of the capacitor in the inverter. This generally results in use of a larger capacitor than necessary because it is difficult to find a capacitor with the proper capacitance and current rating. Typically, the capacitor ranges from approximately 500 microfarads with a volume of approximately 0.9 liters to 1000 microfarads with a volume of approximately 4.0 liters. As a result, when packaged together with an inverter, the capacitor typically occupies 30 to 40 percent of the total volume of the power inverter module. This, in turn, limits the ability to reduce the size, weight, and cost of the power inverter module.